The 2009–10 Druga HNL (also known as 2. HNL) was the 19th season of Croatia's second level football competition since its establishment in 1992. Istra 1961 were league champions and were promoted to Prva HNL at the end of the previous season.
The league featured 14 clubs, playing in a double round robin league system. The season started on 22 August 2009 and ended on 29 May 2010.
Changes from last season
The following clubs have been promoted or relegated at the end of the 2008–09 season:
1Slavonac CO had finished fourth, but had to step back from promotion after they were unable to find a suitable ground for hosting Prva HNL matches. Because of this, fifth-placed Međimurje qualified automatically for promotion and sixth-placed Hrvatski Dragovoljac qualified for the two-legged promotion playoff against last placed Prva HNL team.
2Moslavina finished 15th and also qualified for relegation, but since Slavonac CO was punished for first agreeing to enter Prva HNL and then stepping back from promotion by direct expulsion to 3.HNL, Trogir and Slavonac were the two teams relegated and Moslavina were allowed to stay in 2. HNL.
3 In a two-legged promotion/relegation playoff between Croatia Sesvete (as 12th placed 1.HNL team) and Hrvatski Dragovoljac (as 6th placed 2. HNL team), the former kept their Prva HNL status by beating Hrvatski Dragovoljac with 2–1 on aggregate (0–0, 2–1) on 14 June 2009.
(As of 9 July 2009, two out of the 16 clubs which were supposed to take part in 2. HNL failed to meet UEFA competition requirements and were refused licences. These were Zmaj Makarska and NK Đakovo.)